Computer networks have become ubiquitous. Computer networks include the Internet, Service Provider (SP) networks, private networks, and Local Area Networks (LANs). A network such as an SP network may include peripherally located Provider Edge (PE) routers, each of which couples to one or multiple Customer Edge (CE) routers. For the core network, an ingress PE uses BGP functions to determine the egress PE.
Virtual Private Networks (VPNs) provide a secured means for transmitting and receiving data between network nodes even though a corresponding physical network supporting propagation of the data is shared by many users (and VPNs). In a typical networking environment used for routing data, the environment may include a number of Customer Edge (CE) routers, a number of Provider Edge (PE) routers and a packet-switched network (PSN). Data, encapsulated in layer-2 frames, may be forwarded from a first CE router to a first PE router, from the first PE router across the PSN to a second PE router, and from the second PE router to a second CE router. A Pseudowire (PW) may be utilized to transfer data across the PSN. A Pseudowire is a mechanism that emulates attributes of a service such as Asynchronous Transfer Mode (ATM), Frame Relay (FR), Point-to-Point Protocol (PPP), High Level Data Link Control (HDLC), Synchronous Optical Network (SONET) Frames or Ethernet over a PSN. The functions provided by the PW include encapsulating Protocol Data Units (PDUs) arriving at an ingress port, carrying them across a path or tunnel, managing their timing and order, and any other operations required to emulate the behavior and characteristics of the particular service. In a particular embodiment, PWs are used to carry ingress layer-2 traffic from an ingress PE router to an egress PE router, and then forward the layer-2 traffic out of an egress port of the egress PE router.
The signaling and encapsulation techniques for establishing Single Segment Pseudowires (SS-PWs) between a pair of Ultimate PEs (U-PEs) is well known. In some cases an SS-PW is insufficient. In such a case, a Multi-Segment Pseudowire (MS-PW) composed of more than one SS-PW, traversing one or more Switching Point PEs (SP-PEs) may be used.